1. Field of the Invention
The present invention relates to a sound level meter in which the output voltage of the microphone is supplied to a voltage-frequency converter by way of an exponential circuit, and more particularly to such a sound level meter in which the output of the voltage-frequency converter controls a binary counter having an indicator unit associated therewith and reading directly on a dB scale.
2. Description of the Prior Art
Integrating sound level meters of the type generally described above are known in the art. For example, one may refer to the publication "News From Rohde & Schwarz," Volume 68, Pages 9-12, which is published in English by Rohde & Schwarz, 8000 Muenchen 80, Germany, and fully incorporated herein by this reference. In the sound level meter disclosed in this publication, a dose of noise is measured and indicated by way of a binary counter having a common decimal numerical indicator and, simultaneously, the respective measuring duration is measured and indicated by way of a further counter. For measurements in accordance with the German Industrial Standards (DIN), a squaring of the measured standardized sound level is required, and thus a squarer is usually provided as an exponentially operating circuit in prior device. In accordance with the United States OSHA standard, an exponentially operating circuit with a factor of 1.2 is required, and the exponentially operating circuit is dimensioned correspondingly differently for such mesurements. When a squaring circuit is utilized, the noise dose value corresponds directly to the square of the measured sound pressure, which is integrated during the measuring duration, and the energy equivalent continuous sound level can be determined by dividing the sound dose value with the measured and indicated measuring duration and, by way of subsequent logarithmic application, in accordance with the prior art formula. These prior integrating sound level meters can be very universally applied due to the simultaneous indication of the respective measuring duration, but they have a drawback in that the evaluation of the result is very difficult. In order to simplify the evaluation-computation process, special computing discs have become known in the art, at which only the sound dose and the measuring duration is adjusted, and the energy equivalent continuous sound level can be read off directly. It is also known in the art to associate such an integrating sound level meter with a micro-computer which automates the computation process, as reported by Neumann in the article Noise-Measuring Practice, in the publication "Contact and Studies" Volume 4, Pages 117-120, published by Kruppke and Wippler, Center for Continuing Education, Academy Esslingen, Encyclopedia Publishing House, Grafenaul/Wurtt, Germany. Briefly, Neumann describes the prior art solution as being very technically detailed and expensive.